A digital microwave transfers a data signal in a wireless manner, and a split digital microwave system is formed by two parts: an indoor unit (Indoor Unit, IDU) and an outdoor unit (Outdoor Unit, ODU). A transfer process of a microwave signal in the split digital microwave system includes: An IDU sends an intermediate frequency (IF) signal to an ODU, the ODU performs up-conversion on the IF signal, amplifies the signal, and then transfers the signal to a next ODU through an antenna. After receiving the signal, the next ODU performs down-conversion on the signal, amplifies the signal, and then transfers the signal to another IDU. The IDU demodulates the received signal, and in this way, the transfer of the microwave signal in the split digital microwave system is implemented.
Referring to FIG. 1, an ODU in a split digital microwave system is generally formed by a transmitting module (Tx module) 11, a receiving module (Rx module) 12, and a duplexer (duplexer) 13. The duplexer is formed by a transmitting filter (Tx Filter) 1301 and a receiving filter (Rx Filter) 1302.
In the prior art, loopback of a radio frequency signal is implemented by using a feature that, in the duplexer, attenuation that is performed by the receiving filter (Rx Filter) on a transmission signal is limited. Specifically, in the duplexer, the attenuation that is performed by the receiving filter (Rx Filter) on the transmission signal is limited, and therefore, a radio frequency signal transmitted by the transmitting module (Tx module) is leaked to the receiving module (Rx module) through the duplexer, thus implementing loopback of the radio frequency signal.
The prior art has the following disadvantages:
In the prior art, the duplexer is used to directly leak the transmission signal, so as to implement the loopback of the radio frequency signal, but the duplexer has transmitter-receiver isolation to some extent, therefore, a signal leaked from the radio frequency signal that is sent by the transmitting module (Tx module) to the receiving module through the duplexer generally has small power. Moreover, due to a frequency response characteristic of the receiving filter of the duplexer, when signals with different transmission frequencies and the same transmission power are leaked to an entrance of the receiving module, power of the signals is different, and furthermore, the receiving module requires different minimum receiving power for different service modes. In this way, loopback of signals only at a part of frequencies and in a part of service modes may be implemented.